Electrical timing circuit



March 3, 1942. M. G. NELSEN I 2,214,992

ELECTRICAL TIMING v CIRCUIT Filed Feb. 26, 1940 2 Sheets-Sheet 2 56 90Z--d|- A I! 2 1 3 5P g 56 W; 48 5O 5 6O Patented Mar. 3, 1942 ELECTRICALTIMING CIRCUIT Marvin G. Nelsen, Chicago, Ill., assignm- GuardlanElectric Manufacturing Company, Chicago, 11]., a corporation of IllinoisApplication February 20; 1940, Serial No. 320,982

10 Claims.

The present invention relates to an electrical control circuit of theclass commonly referred to as "timer circuits. The function of suchcircuits is to cause current flow, or cessation of current flow, in somepart of the circuit for a definite and predetermined length of time. Anycurrent or voltage actuated device, as, for example, an electromagneticrelay, may be inserted in the con trolled part of the circuit, toperform switching or other mechanical or electrical operations,responsive to current flow or cessation .of current flow in that part ofthe circuit.

Some of the previous devices employed to give timed control ofelectrical circuits have used clockwork or similar mechanisms. Suchmechanisms require winding or require an electric motor, and aresubject, as is well known, to wide variations in accuracy due totemperature, dirt, faulty workmanship, improper maintenance, etc.

Timer circuits employing electron tubes have also been devised, but haverequired auxiliary apparatus for supplying direct current. Suchauxiliary apparatus obviously entails greater expense in first cost andupkeep, as well as adding to the space and weight requirements.

An object of my invention is to provide a circuit of this characterwhich shall'be operable from an alternating current source and whichdoes not require any auxiliary apparatus to provide a direct currentsupply.

Another object is to provide a timing circuit whereby the time intervalcan be conveniently selected or varied by a simple control means.

Still another object is to provide a control circuit which shall have ahigh degree of consistency in operation, that is, a circuit in which thetimed period shall have substantially the same duration in consecutiveoperationsof the'device, for the same setting of the control means.

A further object is to provide a circuit which is readily adaptable tobeing made up in commercial form, and having adjustment means wherebythe commercial variations in the elements of the circuit can beconveniently com pensated for.

Another object is to provide a circuit whereby a wide range of selectionin the duration of the timed interval may be had.-

With these and other objects in view, my invention with respect to itsfeatures which I believe to be novel and patentable will be pointed outin the claims appended'hereto. For a better detailed understanding ofthe invention, and further objects and advantages thereof, reference ismade to the following description and to 55 the accompanying drawings,wherein such further objects will definitely appear, and in which-Figure l is a symbolic representation of an electrical circuit embodyingmy invention.

Figure 2 shows a modified and somewhat simplified form.

Figure 3 is a graphical representation of the time variation ofpotential diiference between certain points in the circuit.

In the accompanying drawings, I have used the reference numeral ID toillustrate an electron tube having a cathode, a grid l4 and an anode orplate IS. The cathode I2 may be of the filament type or may be of theindirectly heated type. In the drawings, I have shown a cathode of thefilament type which is heated by being connected in circuit with thesecondary winding I8 of a step-down transformer. The primary 20 of thestep-down transformer is connected to the supply wires 22 and 24. When atransformer is used in this manner for heating the cathode, it

will be understood that the supply must be alternating current. Thecircuit is operable from a direct current supply, but in that case thestepdown transformer cannot be used, and suitable resistance means mustbe interposed between the supply wires and the filament to limit thefilament current, as is well known in the art.

My circuit is adapted for use with electron tubes of several types. Thecommon high vacuum or hard" tube may be employed, but I have found thatmore consistent and satisfactory results are obtained with the gaseoustubes of the general class represented by the so-called Thyratron andgrid-glow tubes. Of the common tubes of this class, either the triode orthree element type, or the four element or shield-grid type can beemployed in my circuit.

In the form of my circuit shown in Figure 1, the cathode I2 is connectedby a wire 25 to the resistor 21, the condenser 29, the condenser 52, andthe resistor 42. The other terminal of the condenser 52 leads to thecommon terminal 3| of a single pole, double throw switch. A wire 40connects the grid I4 and the resistor 42 to one terminal of the switch.

The resistor 21 is preferably of the potentiometer type, having a tap orslider which is adjustable along the resistance. This tap is connectedby a wire 35 tothe condenser 29 and to a terminal 31 of the switch. Theswitch may conveniently be of the push button or spring biased type, inwhich the common terminal 3| normally engages the terminal 33, but.disengages terminal 33 and moves into contact with terminal 31 when thebutton is pressed.

The resistor 21 is connected to supply line 22, and supply line 24 isconnected by a wire 23 to the coil of a relay 30. A wire 35 leads fromthe coil of the relay to the plate I oLthe tube Ill. It will usually befound desirable to provide a condenser 32 in shunt across the relaycoil.

Practical operation In explaining the operation of the form of mycircuit shown in Figure 1, it may be well to start with the condition ofoperation in which the switch terminals 3| and 33 are in contact.Assuming this to have been the case for some appreciable time, it maythen be further assumed that the grid [4 is at substantially the samepotential as the cathode l2. In this situation, electron current willflow from the cathode l2 to the plate 16 during the portions of thevoltage cycle in the supply lines 22 and 24 during which the line 22 issufiiciently negative with respect to the line 24 to cause conductionthrough the tube. During the parts of the cycle when an oppositepotential exists, the rectifier action of the tube will prevent any flowof current. Consequently there will pass through the wires 23 and 35 apulstating, unidirectional current. This current will pass through therelay coil 30 and will cause attraction of the armature 54. Thecondenser 32 is shunted across the relay coil 30 in order to smooth outthe pulsations, and thus to reduce chattering and heating of the relay.This condenser may be of the electrolytic type.

The pulsating unidirectional current which flows through the wires 28and 35 flows also through the wire and the resistor 21, the latterelements being a part of the same series circuit. The current flowingthrough the resistor 21 will result in a potential difierence or 9.voltage drop between the terminals 01' the resistor which are connectedto the wires 25 and 22, respectively. The value of the voltage appearingbetween the wire 25 and wire 35 will depend upon the location of the tapor slider on the resistor 21. Between the two latter points, thecondenser 23 is provided. It may be an electrolytic condenser, and ispreferably of large capacity, its function being to maintain arelatively uniform voltage across its terminals throughout the supplyvoltage cycle.

To actuate my timer circuit, the element 3| of the switch is thrown tocontact the switch terminal 31. This places the condenser 52 in shuntwith the condenser 29 and a portion of the resistor 21. The condenser 52will then be charged to the potential existing across the terminals ofthe condenser 29, and the terminal of the condenser 52 which isconnected to the switch element 3i will be at a negative potential withrespect to the terminal that is connected to the wire 25.

The switch is then released, to bring the moving element 31 into contactwith the terminal 33, thus placing the charged condenser 52 in shuntwith the resistor 42.

The potential diiierence between the terminals of the charged condenserwill result in a flow of current from the condenser through the resistor42. Because of the voltage drop across the resistance while this currentflows, the grid [4 will no longer be at the same potential as thecathode l2, as initially assumed, but will be negative with respectthereto.

, would give a timed interval of ten seconds.

The negative bias on the grid at the instant the 7 switch is thrown toplace condenser 52 in shunt with resistance 42 will be the same as thevoltage to which the condenser 52 was charged. This grid bias must besuiiicient to reduce the plate current in the wire 36 to a' value atwhich the relay 30 will drop out, i. e., will release the armature 54.In the case of gaseous tubes, this means a bias voltage at which thetube will be non-conducting.

Throwing the charged condenser 52 in shunt with the resistance 42 thuscauses release of the armature 54 and initiates the timed interval. Anysuitable contact-making means may be operated by the armature, forcontrolling an electrical circuit or other apparatus as desired. InFigure l, for example, a single pole, double throw arrangement is shown.The circuit including terminals and 53 will be closed when the rea layis energized, open when it is de-energized. The circuit includingterminals and 50 will be open when the relay is energized, closed whenthe relay is de-energized.

As current flows from the condenser 52 through the resistor 42, thecharge of the condenser will gradually be dissipated, and the terminalvoltage of the condenser will decrease. Since the grid I4 is at the samepotential as one terminal of the condenser, and the cathode I2 is at thesame potential as the other terminal of the condenser, the diil'erenceof potential between the grid and cathode, i. e., the grid bias, willsimilarly decrease.

The nature of the decrease in voltage is shown in Figure 3, where thecurve R indicates the time variation in grid bias for a given value R ofthe resistance. The value of voltage to which condenser 52 is chargedmay be indicated as E, and the initial bias applied to the grid at thebeginning 01' the interval will therefore be E.

As the grid bias decreases, it will fall ultimately below some value Aat which the electron tube Ill will pass suflicient plate current toactuate the relay 30. Actuation oi the relay consists of attraction ofthe armature 54 and operation of the associated contact means. Thisaction terminates the timed interval. Where a Thyratron type tube isused, the value A represents the grid bias at which the tube wouldbecome conductive.

The value of grid bias A at which actuation of the relay will occur isrepresented in Figure 3 by the dotted horizontal line. When theresistance 42 has the value R, for example, the timed interval will be 2seconds-the time elapsing between the instant of application of thenegative grid bias E, and the instant when the grid bias has decreasedto the value A.

If the value of the resistance 42 be increased, the charge of condenser52 will be dissipated less rapidly, and the duration of the timedinterval will be increased. If the value of the resistance be doubled,for example, then the time variation of grid potential will be asrepresented by the curve 2R, from which it may be seen that the timedinterval will be four seconds. As indicated by the curve 5R, aresistance of five times R If the resistor 42 be variable and suitablycalibrated, therefore, the user can quickly and conveniently make theadjustment necessary for any desired time interval.

The duration of the timed interval can also be varied by changing thevoltage to which the condenser 52 is charged. This voltage must alwaysbe greater than the value A, but with that limitation it may be variedthroughout the range available bychanging the location oi the tap on theresistor 21. If the tap is moved toward the end of resistor-21 which isconnected to the wire 25, the voltage will be reduced. 1 For this newvoltage, which may be designated as E, the variation of grid-cathodepotentials when the charged condenser 32 is shunted across the resistor42 will have new values. 1 I

For example, it was indicated above that when the charging value isE;with the resistance-52 having a value-of R, the grid-cathode potentialwould fall below A in about ten seconds, as represented in Figure 3.With a charging voltage of E, and a resistance value oi'iR, thegrid-cathode potential would vary as indicated by the curve bolicmanner. In actual practice, it is preferably a spring actuated switch inwhich the moving elements 48 and 50 normally engage the terminals 44 and28, respectively, but can be momentarily moved to a position engagingthe terminals 33 and 34, respectively. When released, the movingelements will .then return immediately to the 'normalposition in contactwith the terminals and 23. The particular type of switch, however,doesnot constitute a partof my invention, as any suitable type may/be used,and I v have merely described .a form which is most convenient inoperation.

- plained for Figure 1 above.

'in the wires 23 andii, a diflerence of potential IR-E', resulting in atimed interval of approximately eight seconds.-

If the resistor 42 is variable, its control and that of the slider onthe resistor 2'! can be madeavailable to the operator, making possible avery wide range in the durationof the timed intervals. On the otherhand, it may be desirable to make only one of the controls accessible tothe ordinary user of the device. A knob for the var iable resistor .42may be brought out on a control panel, whereas the tap adjustment on theresistor 21 is only made at the factory. The tap adi'ustment in such acase-would constitute convenient means for adjusting the operation ofthe circuit to specified standard conditions, thus compensating forcommercial variations in the elements employed'in the circuit, as forexample, in the resistors used as element 42, or in the condensers usedas element 52.

The condenser 52 is preferably one having mica or paper dielectric,because a very low leakage characteristic is desirable, and it isimportant that the amount of charge absorbed by the condenserv for agiven applied voltage shall be consistent to a high degree. The relaycan be of any type which will actuate the armature 54 when the normalplate current of the electron tube III flows in the wires 28 and 36. Bynormal plate current is meant the current which flows when the grid isat cathode potential.

The winding of the relay 3!! necessarily has some resistance, and, hencewhen current flows through it there will be 'apotential differencebetween the terminals. This fact constitutesthe basis for the form of mycircuit shown in Figure 2. Where the resistance of the relay is suchthat the voltage drop across it is greater than the value A, it ispossible to eliminate the resistor 21 and the condenser 28 shown inFigure 1.

As will be seen in Figure 2, the cathode I2 is connected to the supplywire 22, to one terminal of the variable resistor 42, and to oneterminal 26 of a double pole, double 'throw switch. The supply wire 24is connected by a wire 28 to the relay coil 30, the condenser 32 and toa terminal 34 of the double pole double throw switch.

The plate l6 of the electron tube is connected by a wire 36 to the otherterminal of the relay coil 30 and the condenser 32, and also to aterminal 33 of the double pole double throw switch.

The grid l4 of the electron tube I0 is con- The principle of operationof the circuit in Figure 2 is substantially the same as that ex- Whencurrent flows exists across the terminals-of the relay 30, and henceacross terminals 34 and "of the switch. The condenser 32 maintains thispotential substantially uniform during the supply voltage cycle.Operating the double throw switch shunts thecondenser 52 across theterminals 34 and,

' If the relay is connected into the circuit in place of the resistor21, Figure 1, then a singlepole and charges the condenser to thepotential existing across those terminals. Release of the switch thenshunts the charged condenser across the grid resistor 42, and the resultis the same as above described in connection with Figure 1'." T

A double pole switch is necessary only when the relay is located in theline from the plate 18- to the supply wire 24 as shown in the drawings.

switch can be used, as that figure shows.

The time control circuit which I have described has many'usefulapplications: 'It maybe used, for example, in photographic work, forcontrolling exposure times- The relay contacts may close the circuitwhich actuates an electrically operated shutter, as on a camera, or mayclose the circuit which supplies the light source,'as' in printing'orenlarging equipment.

The control, thus provided is flexible, convenient, readily adjustablethroughout a wide range, and capable of reproducing consistently thesame timed interval for a given setting of the adjustable elements. Ithas no moving parts in the ordinary sense, and requires a minimum ofcare and attentio Although I have above described the element 42 as aresistance, an imp nce having characteristics othergthan those of afpureresistance can be employed at this point in the circuit, and the timedinterval can be varied by changing the value or the character of theimpedance.

[For example," the element 42 may be an inductnected by a wire 40 to aterminal of the variable resistor 42 and to another terminal 44 of thedouble pole double throw switch, which includes movable switch elements43 and 50. Connected across the moving elements 48 and 50 of the switchis the'condenser 52. A

The double pole double throw switch has been shown in the drawings inthe customary sym- 75 1. In a time control circuit, an electron tube aance, or may be a series or parallel combination of inductance andresistance. The curves shown in Figure 2' would no longer apply, but thecircuit would still have utility as a timing control.

Similarly, I havedescribed the element 52 as a a condenser, but anydesired combination of circuit elements having a capacitive impedancemay be employed in lieu of the single condenser shown.

Although I have herein shown and described a preferred embodiment of myinvention, manifestly it is capable of modification and rearrangementwithout departing from the spirit and scope thereof. I do not,therefore, wish to be understood as limiting this invention to theprecise embodiment herein disclosed, except as I may be so limited bythe appended claims.

I claim as my invention:

having a cathode, anode and grid, a source of potential, a currentactuated device, a resistor, said cathode, anode, current actuateddevice and resistor being connected in series with said source ofpotential, a condenser, discharge means connected between said grid andsaid cathode, said discharge means being adapted to discharge saidcondenser when placed in shunt therewith, and manually operable meansconsecutively shunting said condenser across a portion of said resistorand then across said discharge means.

2. In a time control circuit, an electron tube having a cathode, anodeand grid, a resistance connected between said grid and said cathode, asource of potential, impedance means including a current actuateddevice, said cathode, anode and impedance means being connected inseries with said source of potential, a condenser shunted across atleast a portion of said impedance means, a second condenser, and meansoperable to charge said second condenser by shunting it across saidportion of said impedance means and further operable to discharge saidsecond condenser by shunting'it across said resistance.

3. In an electrical circuit, an electron tube having a cathode, an anodeand a grid, a resistor connected between said grid and said cathode, asource of potential, a current actuated device, said cathode, anode andcurrent actuated device being connected in series with said source ofpotential, a capacitive'impedance, and means whereby said capacitiveimpedance may be selectively shunted across said current actuated deviceor across said resistor.

4. In an electrical circuit, an electron tube having a cathode, an anodeand a grid, a resistor connected between said grid and said cathode, asource of potential, a current actuated device, said cathode, anode andcurrent actuated device being connected in series with said source ofpotential, a capacitive impedance, a condenser in shunt with saidcurrent actuated device, and means whereby said capacitive impedance maybe selectively shunted across said current actuated device or acrosssaid resistor.

5. In an electrical circuit, an electron tube having a cathode, an anodeand a grid, a resistor connected between said grid and said cathode, asource of potential, a current actuated device, said cathode, anode andcurrent actuated device being connected in series with said source ofpotential, a capacitive impedance, and means for sequentially shuntingsaid capacitive impedance across said current actuated device and saidresistor, whereby said capacitive impedance first becomes charged to thepotential existing across the terminals of the current actuated device,so that upon subsequently being shunted across the resistor currentflows from the capacitive impedance through said resistor for imposingnegative bias on the grid, to reduce current flow through the currentactuated device to render said current actuated device inoperative for apredetermined period of time.

6. In an electrical circuit, an electron tube having a cathode, an anodeand a grid, a resistor connected between said grid and said cathode, asource of potential, a current actuated device, said cathode, anode andcurrent actuated device being connected in series with said source ofpotential, a capacitive impedance, and means for sequentially shuntingsaid capacitive impedance across said current actuated device and saidresistor, whereby said capacitive impedance nrst becomes charged to thepotential existing across the terminals of the current actuated device,so that upon subsequently being shunted across the resistor currentflows from the capacitive impedance through said resistor for imposingnegative bias on the grid, to reduce current flow through the currentactuated device to render said current actuated device inoperative tor apredetermined period of time, said resistor being manually adjustablefor varying the predetermined time interval during which said currentactuated device is inoperative.

7. In an electrical circuit, an electron tube having a cathode, an anodeand a grid, a source or potential, a current actuateddevice, saidcathode, anode and current actuated device being connected in serieswith said source oi potential, a capacitive impedance, means wherebysaid capacitive impedance may be selectively shunted across said currentactuated device or across said cathode and grid, and a variableimpedance connected between said grid and said cathode whereby the timerate of discharge of said capacitive impedance may be selectivelycontrolled.

8. A control circuit including an electron tube, cathode, grid and anodeelements in said tube, an impedance connected between said grid and saidcathode, a relay, a connection between said anode and one terminal ofsaid relay, a source of potential, a connection between said cathode andone terminal of said source of potential, a connection between the otherterminal of said source of potential and the other terminal 0! saidrelay, a condenser, and means for shunting said condenser across saidrelay, and subsequently disconnecting said condenser from said relay andshunting said condenser across said impedance.

9. A control circuit including an electron tube, cathode, grid and anodeelements in said tube, an impedance connected between said grid and saidcathode, a relay, a connection between said anode and one terminal ofsaid relay, a source of potenial, a transformer connected to said sourceof potential and to said cathode for heating said cathode, a connectionbetween said cathode and one terminal of said source of potential, aconnection between the other terminal of said source of potential andthe other terminal of said relay, a condenser, and means for shuntings'aid condenser across said relay, and subsequently disconnecting saidcondenser from said relay and shunting said condenser across saidimpedance.

10. In a time control circuit, a rectifier, a source of potential, acurrent actuated device and a resistance connected in series, controlmeans in said rectifier, terminals for said control means, said controlmeans effecting a reduction in current flow through said rectifier whena potential exceeding a given'value is applied to said terminals, acondenser shunted across at least a portion of said resistance, a secondcondenser, a second resistance, connected across said terminals of saidcontrol means, and means operable to charge said second condenser byshunting it across said portion of said first mentioned resistance andfurther operable to discharge said second condenser by shunting itacross said second resistance.

MARVIN G. NELSEN.

